This invention relates to variable pitched tread for off-road tires, more specifically, pitched treads for very low inflation pressure ATV tires.
Repeating tread patterns on vehicle tires designed for on-road usage has long been a source of noise and vibration problems. Changing the arrangement of the tread elements in terms of varying multiple sizes of the tread elements in a predetermined arrangement has long been a practice to reduce tread noise. This tread element size change is commonly referred to as xe2x80x9cpitchingxe2x80x9d.
In recent years, the practice of pitching off-road tires has been contemplated for farm tires. U.S. Pat. Nos. 5,733,394 and 5,843,248 assigned to The Goodyear Tire and Rubber Company teach the value of pitching an agricultural tire for reduced vibration caused by lug impact. Lug impact vibration is commonly most noticeable as a first harmonic peak amplitude type of vibration.
The advantages of pitching farm tires having relatively long bars or lugs is now clearly recognized.
A new class of vehicle tires where pitching heretofore has been avoided is the all-terrain vehicle tire. These tires are operated at very low pressure, typically below 7 psi (0.5 bar), generally less than 4 psi (0.3 bar), with 3 psi (0.20 bar) being most common.
These tires are generally quite small having nominal rim diameters of 12.00 inches (30.5 cm) down to about 6.00 inches (15 cm). The tires are operated at such a low pressure because they must have a very low spring rate. The tires are a key component of the all-terrain vehicle""s suspension system. These otherwise very soft riding tires must exhibit excellent off-road traction and, accordingly, they employ numerous traction elements yielding a tread having a very low net-to-gross ratio. Like drive axle tractor tires, the traction elements contact surface area is quite small. Unlike drive axle tractor tires, the ATV treads generally use very short traction elements placed on a tread circumference that is typically three times or more smaller than a drive axle tractor tire. Not unexpectedly, the ATV tire designers were quite skeptical about the value of tread pitching. It was doubtful that any real benefit could be achieved in a tire application wherein the vehicle""s noise was so loud that the tire noise could barely be discerned.
As ATV vehicles have evolved, a new generation of more environmentally friendly vehicle has developed. Noise damping of the mufflers and engines have resulted in much quieter vehicles. Noise pollution from these vehicles can be dramatically reduced. For hunters and other ATV enthusiasts, noisy ATV vehicles are detrimental.
Challenged with the need to reduce tire noise and vibration at all speed ranges up to 50 mph (80 kph), the ATV tire designer must look to tread patterns which can run much quieter without sacrificing traction.
It is an object of the present invention to have a low pressure ATV tire with a significant tread noise reduction.
It is another object of the present invention to accomplish this noise reduction in a way which is unobtrusive.
An all-terrain vehicle tire (10) has an annular tread (40) and a casing (12) disposed radially inwardly of the tread (40). The casing (12) has a pair of radially inner bead portions (20), a pair of sidewalls (22), one sidewall (22) extending between each bead portion (20) and the tread (40), and a radially inner air chamber extending around the inner periphery of the tire (10).
The tire (10), when mounted on a rim, has an inflated operating pressure in the air chamber of 7 psi (0.5 bar) or less.
The tire (10) has a plurality of spaced tread blocks or traction elements (44) extending radially outwardly from a tread base (42). The blocks or traction elements (44) are arranged in an array of 20 or less total pitches, the pitches having at least three distinct pitch lengths of small (S), medium (M), and large (L); wherein the ratio of large (A) to small (S) is at least 1.1 to 1.
The all-terrain vehicle tire (10) has a nominal rim diameter (D) of less than or equal to 12.00 inches (30 cm) with a normal operating pressure of about 4 psi (0.3 bar).
Preferably, the pitches small (S), medium (M) and large (L) are arranged in the array of 20 pitches or less such that no circumferentially adjacent pitch is more than 10% larger or 10% smaller than the medium pitch (M).
In the preferred invention, the small (S), the medium (M) and the large (L) pitch lengths are arranged in a sequence as follows: SMMMSMSMLMMLMSMLLLM. Alternatively, the sequence of MSMLMSMLMSMLMSMLMSM. Most preferably, the ratio of small (S), medium (M), and large A) pitch lengths satisfies the size ratio of 9:10:11.
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of its section height (SH) to its section width (SW).
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire shaped, with or without other reinforcement elements such as an annular tensile member, flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
xe2x80x9cBelt reinforcing structurexe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 27xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cBias plyxe2x80x9d means a tire having bias angled carcass, the angle of the cords being about 25 to 50xc2x0 relative to the equatorial plane of the tire. Each adjacent ply has cords equal but oppositely oriented.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCasingxe2x80x9d means the tire structure apart from the tread and undertread, but including the sidewalls.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width.
xe2x80x9cDesign rim widthxe2x80x9d is the specific commercially available rim width assigned to each tire size and typically is between 75 and 90% of the specific tire""s section width.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.
xe2x80x9cInnerxe2x80x9d means toward the center of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cLeadingxe2x80x9d refers to a portion or part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the preferred direction.
xe2x80x9cNet-to-gross ratioxe2x80x9d means the ratio of the tire tread rubber that makes contact with a hard flat surface, divided by the area of the tread located between the lateral edges of the tread including non-contacting portions such as grooves as measured 360xc2x0 circumferentially about the tire when the tire is inflated and under normal load conditions.
xe2x80x9cNormal Inflation Pressurexe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal Loadxe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial ply tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection Heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection Widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.